Allergy and Anaphylaxis Flashcards
What is anaphylaxis?
An exaggerated immune mediated hypersensitivity reaction that leads to systemic histamine release, increased vascular permeability and vasodilation.
How does anaphylaxis present?
- Rapid onset and progression of Sx
- Life threatening compromise of:
- Airway (breathing / swallowing / stridor)
- Breathing (SOB, hypoxemia, resp arrest)
- Circulation (tachycardia, hTN, decreased urine output) - Involvement of skin (erythema, urticaria) / mucosa (angiooedema, obstruction, GIT Sx)
What are the most common allergens precipitating anaphylaxis?
- Food (nuts, seafood)
- Stings
- Drugs (penicillin, NSAIDs, ACEi, anaesthetics)
- Contrast media
- blood products
- latex
DDx anaphylaxis?
- Asthma
- Septic shock
Immediate Mx anaphylaxis?
IMMEDIATE
- Airway control + O2
- 0.5mL Adrenaline 1:1000
- Remove agent
- IV Fluids: bolus 1000mL crystalloid
- Monitoring
Secondary treatment anaphylaxis?
- Diphenhydramine (Benadryl) 50mgIM or IV q4-6h
- Methylprednisolone 50-100mg IV
- Salbutamol if bronchospasm
When and why is it important to monitor patient after resolution of anaphylaxis?
Monitor for 4-6h ED; then r/v LMO 24-48h
Can have biphasic rxn up to 48h later.
Medications post anaphylaxis?
3 day course:
i) H1 antagonist (cetirizine or benadryl)
ii) H2 antagonist (ranitidine)
iii) corticosteroids (prednisone 50mg for 5/7)
What is an allergy?
Innappropriate/harmful mine response to foreign substances that are otherwise not harmful, mediated mostly by IgE.
What are allergens?
Generally proteins that elicit an IgE response in allergic individuals.
What is a clinical allergy?
Clinical allergy = symptoms + demonstration of specific IgE (skin test or RAST)
What are the diagnostic allergy tests?
- Skin prick tests
- Serologic assays (e.g. RAST)
- Challenge testing
What are the advantages of SPT?
- Highly sensitive
- in vivo allergen exposure
- Convenient; results in
Disadvantages of SPT?
- Potential for anaphylaxis
- May lack specificity (sensitised by asymptomatic individuals; irritant false positive rxns)
- Specialist clinic required
How do serologic assays work?
Measure allergen specific IgE.
Allergen
What are the advantages of in vitro assays?
E.g. IgE serum - RAST etc.
- Availability (GPs can do)
- Safety
- Specific at high level
- Standardised
Disadvantages of in vitro assays?
- Interpretation depends on pre test probability (FP 5-10%)
- Elevated total IgE (e.g. eczema) may give false postives
- medicare only subsidised 4 tests at one time
When are challenge tests used?
When RAST and SPT negative/discordant and good clinical story.
How are allergies treated?
Allergen SPECIFIC: -allergen avoidance -allergen specific immunotherapy NON SPECIFIC -antihistamines/ steroids -adrenaline -leukotriene antagonists -anti IgE Abx (omalizumab)
What is allergen immunotherapy?
S/C allergen injections. Only current allergy therapy to provide improvement / cure.
Efficacy limited by side effects.
Main indication for SC injection immunotherapy?
- Venom allergy (bee, wasp)
- Allergic rhinitis
- Mild, well controlled allergic asthma
What are the RFx for fatal food related anaphylaxis?
- Associated asthma
- Lack of epipen
- young adults
- EtOH
- Extreme sensitivity
Describe the mechanism of bee sting?
- Sting via barbed modified ovipositor which is left in the skin
- Only sting once
- Each sting deposits 35-200mcg venom
Describe wasp sting.
- Nests in concealed locations
- Most aggressive toward end of summer
- Can sting multiple times
- 10-20mcg venom per sting
